IT DOESN'T TAKE MUCH TO REACH A RUNNER'S HIGH

Some joggers report a "runner's high" after exercising for extended periods, but Canadian researchers have found that longer runs are not always better when it comes to mood improvement.

They recruited 69 physically active women from university recreation classes and running clubs and divided them into three groups. Two groups were instructed to get their heart rate up to 70 percent of its maximum while running on an indoor track. One group ran 25 minutes, the other ran 40 minutes. The third group was told to sit in the bleachers for 40 minutes and observe what was happening around them.

Only the 25-minute runners reported a significant increase in tranquillity. Both running groups reported feeling less fatigued than the no-exercise controls, but only the 40-minute runners experienced a statistically significant decrease in fatigue.

Regardless of how long they stayed on the track, runners reported feeling happier and more refreshed after exercising.

Dr. Tim Church, medical director of the Cooper Institute in Dallas, said the findings reinforce the notion that people can reap benefits from a moderate amount of exercise.

"The idea that there are benefits at 25 minutes supports our, and the surgeon general's, idea that it doesn't take that much," he said.

The study -- from the University of Ottawa, University of Alberta and University of Montreal -- will appear in an upcoming issue of the journal Psychology of Sport and Exercise.